1. Field
Aspects of embodiments of the present invention relate to a mask frame assembly used for deposition of a thin film.
2. Description of the Related Art
In general, an organic light emitting display exhibits a wide viewing angle, superior contrast, and fast response speeds. The organic light emitting display produces colors by injecting holes and electrons respectively in an anode and a cathode and combining the holes and electrons in a light-emitting layer. The organic light emitting display has a deposition structure in which the light-emitting layer is inserted between the anode and the cathode. However, since it is difficult to obtain a high efficiency light emission from the deposition structure, an intermediate layer, such as an electron injection layer, an electron transport layer, a hole transport layer, and a hole injection layer, between each electrode and the light-emitting layer needs to be selectively and additionally inserted.
The electrodes and the intermediate layer including the light-emitting layer of the organic light emitting display may be formed using a variety of methods, such as a deposition method, for example. To fabricate the organic light emitting display by using the deposition method, a fine metal mask (FMM) having the same pattern as that of a thin film to be formed on a substrate is aligned and the thin film having a desired pattern is formed by depositing a raw material for the thin film.
As the size of the FMM increases, an etching error in forming a thin film pattern increases and a sagging phenomenon at the center portion of the FMM due to the weight of the FMM itself becomes severe. To address this matter, a split mask, which is made by splitting a mask into a plurality of strips and then attaching the strips to a frame is preferred. Compared to a one-piece mask, the sagging phenomenon may occur in the split mask less severely. When attached to the frame, the split mask is welded to the frame by being tightly pulled in a lengthwise direction.
However, when the split mask is welded to the frame in a tension state as described above, although a tight tension force is applied to the split mask in a lengthwise direction in which the split mask is pulled, a contraction force is applied in a widthwise direction such that wrinkles in a wave form are generated in the split mask. In particular, as a mask is made thinner in order to reduce shadow that affects the thickness of a deposition film, the thickness of a mask is merely 20-40 μm and thus wrinkles are easily generated in the mask due to the contraction force in the widthwise direction. As such, when the wrinkles are generated, the mask is not closely attached to the substrate in some positions so that precise patterning may not be possible.
However, when the mask is attached directly to the frame without being pulled, it is not possible to form a precise pattern because of the mask sagging phenomenon described above. Therefore, a method of preventing or reducing generation of wrinkles when a mask is fixed to the frame by being tightly pulled in a lengthwise direction thereof is needed.